The present invention relates to black magnetic iron oxide particles each having a polyhedral shape comprising magnetite particles having a high blackness.
When using the black magnetic iron oxide particles of the present invention, it is possible to produce a magnetic toner having a high blackness.
As one of the conventional methods for developing electrostatic latent images, there is extensively known and used such a developing method using a so-called “one component system magnetic toner” in which composite particles prepared by mixing and dispersing magnetic particles such as magnetite particles in a resin without using any carrier are used as a developer.
In recent years, with enhancement in performance of electrostatic copying machines, there is an increasing demand for a magnetic toner having a higher blackness as a developer.
The blackness of the magnetic toner largely depends upon a blackness of magnetite to be contained in the magnetic toner. In order to allow the magnetite to exhibit a sufficient blackness when incorporated into the magnetic toner, it is important that a coating film, in particular, a thin coating film, which is formed by using the magnetite, has a high blackness.
Therefore, there is a strong demand for black magnetic particles capable of exhibiting a high blackness even when incorporated into such a thin coating film.
Hitherto, various attempts have been made in order to obtain magnetite particles having a high blackness (refer to Japanese Patent Application Laid-open (KOKAI) Nos. 5-43253 (1993), 9-59025 (1997) and 3-201509 (1991)).